Projection device with p-polarized radiation for head-up display (HUD)

Abstract

A projection device for a head-up display (HUD), comprising at least a windshield (10) having a HUD region (B), comprising an outer glass pane (1) having an outer side (I) and an inner side (II) and an inner glass pane (2) having an inner side (III) and an outer side (IV), wherein the inner side (II) of the outer glass pane (1) and the inner side (III) of the inner glass pane (2) are connected to each other via a thermoplastic intermediate layer (3); and a projector (4) which is aligned with the HUD region (B); wherein the radiation of the projector (4) is predominantly p-polarized, and the windshield (10) has a reflective coating (20) suitable for reflecting the p-polarized radiation; and wherein the reflective coating (20) has There is exactly one silver-based conductive layer (21), a lower dielectric layer (22a) or a layer sequence (22a, 22b, 22c) having a refractive index of at least 1.9 is arranged below the conductive layer (21), an upper dielectric layer (23a) or a layer sequence (23a, 23b, 23c) having a refractive index of at least 1.9 is arranged above the conductive layer (21), the ratio of the optical thickness of the upper dielectric layer (23a) or the layer sequence (23a, 23b, 23c) to the optical thickness of the lower dielectric layer (22a) or the layer sequence (22a, 22b, 22c) is 2.10 to 3.20, and the reflective coating (20) does not include any dielectric layer having a refractive index of less than 1.9.

Description

Technical Field

[0001] The invention relates to a projection device for a head-up display and application thereof. Background Art

[0002] Modern cars are increasingly equipped with so-called head-up displays (HUDs). Using a projector, an image is projected onto the windshield, typically in the area of ​​the instrument panel, where it is reflected and perceived by the driver as a virtual image behind the windshield. This allows important information, such as current driving speed, navigation, or warnings, to be projected into the driver's field of view, allowing the driver to perceive it without having to take their eyes off the road. Consequently, head-up displays can significantly contribute to improving traffic safety.

[0003] HUD projectors operate primarily with s-polarized radiation and illuminate the windshield at an angle of incidence of approximately 65%, which is close to the Brewster angle of the air-to-glass transition (56.5° for soda-lime glass). This presents the problem of the projector image being reflected on both outer surfaces of the windshield. This results in a slightly offset secondary image, a so-called ghost image, appearing in addition to the desired main image. This problem is typically alleviated by arranging the surfaces at an angle to one another, particularly by using a wedge-shaped interlayer for laminating the windshield to form a composite glass pane, so that the main and ghost images are superimposed. Composite glass with a wedge film for HUDs is known, for example, from WO 2009 / 071135 A1, EP 1 800 855 B1, or EP 1 880 243 A2.

[0004] Wedge films are expensive, so the production of composite glass panes for such HUDs is quite expensive. Therefore, there is a demand for a HUD-projection device that does not require a wedge film and can be applied to windshields. For example, a HUD projector can be operated with p-polarized radiation that is essentially not reflected on the surface of the glass pane. Instead, the windshield has a reflective coating as a reflective surface for the p-polarized radiation. DE102014220189A1 discloses such a HUD projection device that operates with p-polarized radiation. As a reflective structure, a single-layer metal layer with a thickness of 5nm to 9nm, for example composed of silver or aluminum, is particularly recommended. WO2019046157A1 also discloses a HUD with p-polarized radiation, in which a reflective coating with at least two metal layers is used.

[0005] US2017242247A1 discloses another HUD projection device with a reflective coating for p-polarized radiation. This reflective coating may include one or more conductive silver layers and a dielectric layer. However, the reflectance spectrum has a significant curvature in the relevant spectral range, resulting in a relatively strong dependence of the reflectance on wavelength. This is disadvantageous for color-neutral HUD projection.

[0006] WO2020083649A1 discloses a projection device for a vehicle, comprising a vehicle side window having a reflective coating and a projector, wherein the radiation of the projector is mainly p-polarized and the reflective coating is suitable for reflecting the p-polarized radiation.

[0007] Information displayed in the HUD, such as speed or the distance to the vehicle ahead, is determined by driver assistance systems integrated into the vehicle. With the continued development of autonomous vehicles, these driver assistance systems are becoming increasingly important, so newly developed vehicle glazing must naturally be compatible with them. Modern driver assistance systems are often referred to as ADAS (Advanced Driver Assistance Systems) and utilize, for example, ultrasound, radar, lidar, and / or camera technology. Depending on the type and application of the sensor, these are also installed in areas of the vehicle glazing, such as behind the vehicle windshield. It should be noted that the corresponding vehicle glazing has good transmittance for the radiation the sensor is intended to detect. Furthermore, these sensors operate with polarization contrast, meaning they utilize different transmittances for s- and p-polarized radiation. A measure of this is the so-called polarization ratio, which is the quotient of the intensity of p-polarized radiation divided by the intensity of s-polarized radiation. Any coatings on the vehicle glazing, such as heating layers or reflective coatings, are typically associated with reduced transmittance. To ensure adequate sensor functionality behind such coatings, for example, the coating can be partially removed. This results in additional process steps and costs in the manufacturing process. Furthermore, the removed areas are reflectively detectable. Summary of the Invention

[0008] Therefore, there is a need for a projection device for HUD with a reflective coating that has high reflectivity for p-polarized radiation and at the same time has sufficiently high transmittance and a high polarization ratio for a camera system located behind the glazing. The object of the present invention is to provide such an improved projection device.

[0009] According to the invention, the object of the invention is achieved by the projection device according to the invention. Preferred embodiments emerge from the further description.

[0010] According to the present invention, p-polarized radiation is used to generate the HUD image, and the composite glass pane has a reflective coating that effectively reflects p-polarized radiation. Because the typical angle of incidence of approximately 65° for HUD projection devices is relatively close to the Brewster angle of the air-to-glass transition (56.5° for soda-lime glass), the p-polarized radiation is barely reflected by the glass pane surface, but rather by the conductive coating. Consequently, ghost images are absent or barely perceptible, eliminating the need for expensive wedge films. Furthermore, the HUD image is recognizable even to the wearer of polarization-selective sunglasses, which typically only allow p-polarized radiation to pass and block s-polarized radiation. The reflective coating according to the present invention produces a high reflectivity for p-polarized radiation in the spectral range of 450 nm to 650 nm, which is relevant for HUD displays (HUD projectors typically operate at wavelengths of 473 nm, 550 nm, and 630 nm (RGB)). This results in a high-intensity HUD image. A single silver layer does not significantly reduce light transmittance, allowing the glass pane to continue to be used as a windshield. The optical thickness ratio of the upper and lower dielectric layer sequences according to the present invention produces a smooth reflection spectrum, thus ensuring a color-neutral display. The favorable reflection properties, in particular the spectral homogeneity, even extend beyond the HUD-relevant spectral range to the spectral range of 400 nm to 680 nm. This not only ensures a good HUD display but also ensures a holistic impression of the front face of the glass pane without disruptive color distortion. This is a major advantage of the present invention. In addition to the favorable HUD properties of the windshield, it also offers optimized sensor compatibility, in particular camera compatibility. In the inventors' experiments, a favorable ratio of p-polarized transmitted light to s-polarized transmitted light was achieved even with a ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence of 2.10 to 3.20. The reflective coating does not include any dielectric layers with a refractive index of less than 1.9. Therefore, all dielectric layers of the reflective coating have a refractive index of at least 1.9.

[0011] The projection device for a head-up display (HUD) according to the present invention comprises at least a windshield with a reflective coating and a projector. As is common in HUDs, the projector illuminates an area of ​​the windshield, where the radiation is reflected toward the viewer (driver), thereby generating a virtual image that the viewer perceives as appearing behind the windshield. The area of ​​the windshield illuminated by the projector is referred to as the HUD area. The projector's beam direction can typically be modified by a mirror, particularly vertically, to adapt the projection to the viewer's body dimensions. The area within which the viewer's eyes must be located at a given mirror position is referred to as the eye-range window. This eye-range window can be moved vertically by adjusting the mirrors, with the entire area thus accessible (that is, the sum of all possible eye-range windows) being referred to as the eye-range window. Viewers within the eye-range window can perceive the virtual image. This naturally means that the viewer's eyes, rather than, for example, their entire body, must be within the eye-range window.

[0012] The projection device for a HUD according to the present invention is particularly suitable for mounting sensors on the windshield, particularly sensors used in ADAS systems. The term ADAS refers to modern driver assistance systems that use environmental sensors based on, for example, ultrasound, radar, lidar, and / or camera technology. One or more of these or other sensors can be mounted in the area of ​​the windshield.

[0013] The technical terms used in the field of HUDs are generally known to those skilled in the art. For a detailed description, reference is made to the paper "Simulations basierte Messtechnik zur Prüfung von Head-Up Displays" by Alexander Neumann of the Institute of Computer Science at the Technical University of Munich (Munich: University Library of the Technical University of Munich, 2012), in particular Chapter 2, "Das Head-Up Display."

[0014] The windshield comprises an outer pane and an inner pane, which are connected to each other via a thermoplastic interlayer. The windshield serves to separate the interior of a vehicle from the exterior environment in a window opening. Within the meaning of the present invention, the inner pane is the pane of the windshield facing the vehicle interior. The outer pane is the pane facing the exterior environment. The windshield is preferably the windshield of a motor vehicle, in particular a passenger car or truck.

[0015] A windshield has an upper edge and a lower edge, and two side edges extending therebetween. The upper edge is the edge intended to point upward in the installed position. The lower edge is the edge intended to point downward in the installed position. The upper edge is often also referred to as the top edge, and the lower edge as the engine edge.

[0016] The outer and inner glass panes each have an outer side and an inner side surface, and a circumferential side edge extending therebetween. Within the meaning of the present invention, an outer side surface is a main surface that, in the installed position, faces the outside environment. Within the meaning of the present invention, an inner side surface is a main surface that, in the installed position, faces the interior. The inner side surface of the outer glass pane and the outer side surface of the inner glass pane face one another and are connected to one another via a thermoplastic interlayer.

[0017] A projector is aimed at the HUD area of ​​the windshield. The radiation from the projector is primarily p-polarized. The reflective coating is adapted to reflect the p-polarized radiation. This creates a virtual image from the projector radiation, which the driver of the vehicle perceives as being behind the windshield.

[0018] The reflective coating according to the present invention has exactly one silver-based conductive layer. Exactly one silver-based conductive layer means that the reflective coating according to the present invention contains only this one silver-based conductive layer and no other silver-based layers. This also includes, according to the present invention, that on the substrate on which the reflective coating is applied, no silver-containing layer is present below or above the reflective coating according to the present invention. A lower dielectric layer or layer sequence is arranged below this conductive layer. Similarly, an upper dielectric layer or layer sequence is arranged above this conductive layer. The upper and lower dielectric layers or layer sequences each have a refractive index of at least 1.9.

[0019] Within the scope of the present invention, the refractive index is in principle given based on a wavelength of 550 nm. The optical thickness is the product of the geometric thickness and the refractive index (at 550 nm). The optical thickness of the layer sequence is calculated as the sum of the optical thicknesses of the individual layers. For example, the refractive index can be determined by means of ellipsometry. Ellipsometers are commercially available, for example from Sentech. The refractive index of the upper or lower dielectric layer is preferably determined by first depositing it as a single layer on a substrate and then measuring the refractive index by means of ellipsometry. In order to determine the refractive index of the upper or lower dielectric layer sequence, the layers of the layer sequence are each deposited separately as single layers on a substrate and the refractive index is then determined by means of ellipsometry. According to the present invention, a refractive index of at least 1.9 can be achieved for each of these single layers. Dielectric layers with a refractive index of at least 1.9 and methods for their deposition are known to those skilled in the art of thin layers. Preferably, physical vapor deposition methods are used, in particular magnetron sputtering.

[0020] If the first layer is arranged above the second layer, this means in the sense of the invention that the first layer is arranged further away from the substrate on which the coating is applied than the second layer. If the first layer is arranged below the second layer, this means in the sense of the invention that the second layer is arranged further away from the substrate than the first layer.

[0021] If a layer is formed on the basis of a material, it consists predominantly of this material, in particular essentially of this material apart from any impurities or dopants.

[0022] According to the present invention, the ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is 2.10 to 3.20. This asymmetry in the optical thickness has been shown to produce a significantly smoother reflection spectrum for p-polarized radiation, resulting in a relatively constant reflectance across the entire relevant spectral range (400 nm to 680 nm). This ensures a color-neutral display of the HUD projection and a color-neutral overall impression of the glass pane. Furthermore, within this small range of optical thickness ratios, a particularly favorable polarization ratio of p-polarized light to s-polarized light has been demonstrated. The polarization ratio is defined as the ratio of the transmittance of p-polarized light to the transmittance of s-polarized light. Sensors, such as cameras, with the reflective coating according to the present invention in their beam path can only perceive light transmitted by the reflective coating. Therefore, high transmittance is required when using sensors behind the windshield. In particular, the transmittance of p-polarized light should predominate over that of s-polarized light and be as high as possible. The polarization ratio of the transmitted light is crucial to avoid glare effects that restrict the camera's field of view under wet road conditions. To suppress these glare effects, the transmittance of p-polarized light must be greater than the transmittance of s-polarized light. The requirements for good HUD image quality necessitate a high reflectance of p-polarized light on the reflective coating, which is in contrast to the high transmittance required for camera applications. The inventors have discovered that within the optical thickness ratios according to the present invention, it is possible to achieve a reflectance of p-polarized light sufficient for HUD applications while simultaneously achieving a favorable ratio of p-polarized light to s-polarized light for light transmitted through the windshield. Thus, within the narrow limits of the mentioned optical thickness ratios, a projection arrangement for a head-up display optimized for camera applications can be achieved.

[0023] The optical thickness ratio according to the invention is calculated as the quotient of the optical thickness of the upper dielectric layer or layer sequence (dividend) divided by the optical thickness of the lower dielectric layer or layer sequence (divisor).

[0024] In a preferred embodiment, the ratio of the optical thickness of the upper dielectric layer or layer sequence to the optical thickness of the lower dielectric layer or layer sequence is 2.14 to 3.10, preferably 2.20 to 3.10, particularly preferably 2.30 to 2.98, in particular 2.50 to 2.97. Particularly good results are achieved thereby.

[0025] Preferably, the polarization ratio of p-polarized light to s-polarized light achieved with the reflective coating according to the present invention is at least 1.28 at a transmission angle of 55°, at least 1.41 at a transmission angle of 61°, and / or at least 1.59 at a transmission angle of 67°. The transmission angle is the angle of radiation transmitted through the windshield. The transmission angle is determined as the angle between the normal to the windshield surface and the transmitted outgoing radiation. The sensor provided behind the windshield is preferably provided at a transmission angle for which the reflective coating is optimized. The aforementioned limit values ​​for the polarization ratio correspond to the technical specifications of the relevant camera system. Particularly preferably, at least two of the aforementioned limit values ​​for the polarization ratio are achieved. In particular, all three of the aforementioned limit values ​​for the polarization ratio are achieved by the reflective coating according to the present invention. This is advantageous because it allows the camera to be used at different transmission angles.

[0026] The windshield of the projection device according to the present invention preferably includes a sensor area. A sensor can be installed in this sensor area so that radiation passes through the reflective coating and is detected by the sensor. The projection device is preferably also provided with a sensor during manufacture, which detects radiation passing through the windshield in the sensor area. However, the windshield of the projection device according to the present invention is also suitable for retrofitting sensors or using a dashboard-mounted camera (also known as a dashcam). The reflective coating according to the present invention is optimized for its compatibility with camera systems, making it possible to install a camera at any location. Removing the cover of the camera window can be omitted.

[0027] If the projection device according to the present invention includes a sensor, the reflective coating is located in the sensor's beam path. The sensor is typically located behind the windshield, i.e., in the vehicle interior when the windshield is installed, and is preferably fixed adjacent to the outer side of the inner window pane. The sensor is preferably an ultrasonic sensor, a radar sensor, a lidar sensor, and / or a camera. The sensor is particularly preferably a camera that detects radiation in the visible range of the spectrum. The reflective coating according to the present invention meets the limit values ​​required by the relevant camera system specifications for the ratio of p-polarized transmitted light to s-polarized transmitted light.

[0028] The reflective coating is preferably applied to the surfaces of both glass panes facing the interlayer, i.e., the interior-facing surface of the outer glass pane or the exterior surface of the inner glass pane. Alternatively, the reflective coating can be disposed within the thermoplastic interlayer, for example, on a carrier film disposed between two thermoplastic connecting films. The reflective coating is transparent, which, within the meaning of the present invention, means that it has an average transmittance of at least 70%, preferably at least 80%, in the visible spectral range and thus does not substantially restrict the view through the glass panes. Partial or even large areas can be provided with the reflective coating, and the windshield can be provided with a reflective coating over essentially the entire surface, which may be preferred for manufacturing reasons. In one embodiment of the present invention, at least 80% of the surface of the glass pane is provided with the reflective coating according to the present invention. In particular, the reflective coating is applied over the entire surface of the glass pane, with the exception of surrounding edge regions and optionally localized regions that, as communication windows, sensor windows, or camera windows, ensure electromagnetic radiation transmission through the windshield and therefore do not have a reflective coating. The surrounding uncoated edge region can, for example, have a width of up to 20 cm. It prevents the reflective coating from coming into direct contact with the surrounding atmosphere, thereby protecting the reflective coating in the interior of the windshield from corrosion and damage.

[0029] Due to the conductive silver layer, the reflective coating according to the present invention has IR-reflecting properties and thus functions as a sun protection coating, which reduces heating of the vehicle interior by reflecting thermal radiation. If electrical contact is made with the reflective coating, such that current flows through it, thereby heating it, the reflective coating can also function as a heating coating.

[0030] A windshield with a reflective coating preferably has an average reflectance of at least 15%, particularly preferably at least 20%, for p-polarized radiation in the spectral range from 400 nm to 680 nm. This produces a sufficiently high-intensity projected image. The reflectance is measured at an angle of incidence of 65° to the surface normal on the interior side, which roughly corresponds to the illumination produced by a conventional projector. The spectral range from 400 nm to 680 nm is plotted to characterize the reflective properties because the viewer's visual impression is primarily determined by this spectral range. Furthermore, it covers the wavelengths relevant for HUD displays (RGB: 473 nm, 550 nm, 630 nm). This high reflectance with a relatively simple layer structure is a major advantage of the present invention. Particularly good results are achieved when the reflectance over the entire spectral range from 400 nm to 680 nm is at least 15%, preferably at least 20%, so that the reflectance does not fall below the specified value at any point within the specified spectral range.

[0031] The reflectance describes the proportion of the total incident radiation that is reflected. It is given in % (based on an incident radiometer of 100%) or as a dimensionless number between 0 and 1 (normalized to the incident radiation). Plotted as a function of wavelength, it forms a reflection spectrum. Within the scope of the present invention, the statements about the reflectance for p-polarized radiation relate to the reflectance measured at an angle of incidence of 65° to the surface normal on the interior side. The information about the reflectance or reflection spectrum relates to reflection measurements performed with a light source that is uniformly illuminated with a normalized radiation intensity of 100% in the spectral range considered.

[0032] To achieve a projector image that is as color-neutral as possible, the reflection spectrum should be as smooth as possible and free of significant local minima and maxima. In a preferred embodiment, the difference between the maximum reflectance occurring and the mean reflectance value, as well as the difference between the minimum reflectance occurring and the mean reflectance value, in the spectral range from 400 nm to 680 nm should be at most 3%, particularly preferably at most 2%. Here, the reflectance for p-polarized radiation, measured at an angle of incidence of 65° to the surface normal on the interior side, is also used. The differences specified are to be understood as absolute deviations in the reflectance (given in %), not percentage deviations from the mean value. Due to the conductive layer of the reflective coating according to the invention, the specified smoothness of the reflection spectrum can be readily achieved with the reflective coating according to the invention.

[0033] Alternatively, the standard deviation in the spectral range from 400 nm to 680 nm can be used as a measure of the smoothness of the reflection spectrum. It is preferably less than 1%, particularly preferably less than 0.9%, very particularly preferably less than 0.8%.

[0034] The desired reflection properties described above are achieved, inter alia, by selecting the materials and thicknesses of the individual layers and the structure of the dielectric layer sequence. The reflective coating can thus be suitably adjusted.

[0035] The reflective coating is a thin layer stack, i.e., a sequence of thin, single-layer layers. This thin layer stack contains exactly one silver-based conductive layer. This silver-based conductive layer imparts the reflective coating with its basic reflective properties and, in addition, its IR reflection and electrical conductivity. This silver-based conductive layer can also be simply referred to as a silver layer. The reflective coating contains exactly one silver layer, i.e., no more than one silver layer, and no further silver layers are arranged above or below it. A particular advantage of the present invention is that the desired reflective properties can be achieved with the silver layer without significantly reducing the transmittance, as would be the case when using multiple conductive layers. However, further conductive layers may be present which do not significantly contribute to the electrical conductivity of the reflective coating but instead serve other purposes. This applies in particular to metallic barrier layers having a geometric thickness of less than 1 nm, which are preferably arranged between the silver layer and the dielectric layer sequence.

[0036] The conductive layer is formed on the basis of silver. The conductive layer preferably contains at least 90% by weight of silver, particularly preferably at least 99% by weight of silver, very particularly preferably at least 99.9% by weight of silver. The silver layer may have dopants, for example palladium, gold, copper or aluminum. The geometric layer thickness of the silver layer is preferably at most 15 nm, particularly preferably at most 14 nm, very particularly preferably at most 13 nm. This makes it possible to achieve favorable reflectivity in the IR range without significantly reducing the transmittance. The geometric layer thickness of the silver layer is preferably at least 5 nm, particularly preferably at least 8 nm. Thinner silver layers can lead to dewetting of the layer structure. The geometric layer thickness of the silver layer is particularly preferably from 10 nm to 14 nm or from 11 nm to 13 nm.

[0037] The reflective coating does not include any dielectric layers with a refractive index of less than 1.9. Therefore, all dielectric layers of the reflective coating have a refractive index of at least 1.9. The inventors have experimentally demonstrated that the use of low-refractive layers, such as silicon dioxide, has a negative effect on the optical thickness ratio and, consequently, unfavorable reflective properties for p-polarized radiation. A particular advantage of the present invention is that the desired reflective properties can be achieved using only relatively high-refractive dielectric layers. Since silicon oxide layers, which have a low deposition rate in magnetic field-assisted cathode deposition, are particularly suitable for low-refractive layers with a refractive index of less than 1.9, the reflective coating according to the present invention can be produced quickly and cost-effectively.

[0038] The reflective coating comprises, above and below the silver layer, a separate dielectric layer or a sequence of dielectric layers having a refractive index of at least 1.9. The dielectric layers can be based, for example, on silicon nitride, zinc oxide, tin-zinc oxide, silicon-metal mixed nitrides such as silicon-zirconium nitride, zirconium oxide, niobium oxide, hafnium oxide, tantalum oxide, tungsten oxide, or silicon carbide. The oxides and nitrides mentioned can be deposited in stoichiometric, substoichiometric, or superstoichiometric amounts. They can also be doped, for example with aluminum, zirconium, titanium, or boron. Layers of these materials having a refractive index of at least 1.9 as single layers are known and can be obtained by those skilled in the art using known methods. These layers are preferably deposited using physical vapor deposition, in particular magnetron sputtering.

[0039] The optical thickness of the upper dielectric layer or layer sequence is preferably 100 nm to 200 nm, particularly preferably 130 nm to 170 nm. The optical thickness of the lower dielectric layer or layer sequence is preferably 30 nm to 100 nm, particularly preferably 40 nm to 65 nm. Good results are achieved in this way.

[0040] In an advantageous embodiment, a dielectric layer is arranged above and below the silver layer, which can be referred to as an anti-reflection layer and is preferably based on an oxide, for example tin oxide, and / or a nitride, for example silicon nitride, particularly preferably based on silicon nitride. Silicon nitride has proven to be advantageous due to its optical properties, its availability and its high mechanical and chemical stability. Silicon is preferably doped with, for example, aluminum or boron. In the case of a dielectric layer sequence, the layer based on silicon nitride is preferably the uppermost layer of the upper layer sequence or the lowermost layer of the lower layer sequence. The geometric thickness of the upper anti-reflection layer is preferably 50 nm to 100 nm, particularly preferably 55 nm to 80 nm, in particular 60 nm to 70 nm. The geometric thickness of the lower anti-reflection layer is preferably 10 nm to 50 nm, particularly preferably 15 nm to 40 nm, in particular 20 nm to 35 nm.

[0041] In addition to the antireflection layer, a further dielectric layer with a refractive index of at least 1.9 may optionally be present. Thus, the upper and lower layer sequences may independently contain an adaptation layer which improves the reflectivity of the silver layer. The adaptation layer is preferably based on zinc oxide, particularly preferably zinc oxide ZnO. 1-δ δ is formed, where 0 ≤ δ ≤ 0.01. The adapting layer preferably further contains a dopant. For example, the adapting layer may comprise aluminum-doped zinc oxide (ZnO:Al). To prevent excess oxygen from reacting with the silver-containing layer, the zinc oxide is preferably deposited in a substoichiometric amount relative to oxygen. The adapting layer is preferably arranged between the silver layer and the antireflection layer. The geometric thickness of the adapting layer is preferably 5 nm to 30 nm, particularly preferably 8 nm to 12 nm.

[0042] A refractive index-increasing layer having a higher refractive index than the anti-reflection layer may also be present, also independently of one another, in the upper and lower layer sequences. This allows the optical properties, in particular the reflective properties, to be further improved and fine-tuned. The refractive index-increasing layer preferably comprises a silicon-metal mixed nitride, such as a silicon-zirconium mixed nitride, a silicon-aluminum mixed nitride, a silicon-titanium mixed nitride or a silicon-hafnium mixed nitride, particularly preferably a silicon-zirconium mixed nitride. The proportion of zirconium is preferably 15 to 45% by weight, particularly preferably 15 to 30% by weight. As alternative materials, for example, WO3, Nb2O5, Bi2O3, TiO2 and / or AlN can be considered. The refractive index-increasing layer is preferably arranged between the anti-reflection layer and the silver layer or between the adaptation layer (if present) and the anti-reflection layer. The geometric thickness of the refractive index-increasing layer is preferably 5 nm to 30 nm, particularly preferably 5 nm to 15 nm.

[0043] In one embodiment of the present invention, exactly one lower dielectric layer with a refractive index of at least 1.9, preferably based on silicon nitride, is arranged below the conductive layer. Similarly, exactly one upper dielectric layer with a refractive index of at least 1.9, preferably based on silicon nitride, is arranged above the conductive layer. The resulting layer sequence, starting from the substrate, is: lower antireflection layer - silver layer - upper antireflection layer. The reflective coating preferably contains no additional dielectric layers. The geometric thickness of the upper antireflection layer is preferably 50 nm to 100 nm, particularly preferably 55 nm to 80 nm, in particular 60 nm to 70 nm. The geometric thickness of the lower antireflection layer is preferably 10 nm to 50 nm, particularly preferably 15 nm to 40 nm, in particular 20 nm to 35 nm.

[0044] In another embodiment of the present invention, a first lower dielectric layer (anti-reflection layer) and a second lower dielectric layer (adaptation layer) are arranged below the conductive layer. Similarly, a first upper dielectric layer (anti-reflection layer) and a second upper dielectric layer (adaptation layer) are arranged above the conductive layer. The refractive index of the anti-reflection layer and the adaptation layer is at least 1.9. The anti-reflection layer is preferably based on silicon nitride, and the adaptation layer is based on zinc oxide. The adaptation layer is preferably arranged between the respective anti-reflection layer and the silver layer, resulting in the following layer sequence starting from the substrate: lower anti-reflection layer - lower adaptation layer - silver layer - upper adaptation layer - upper anti-reflection layer. The reflective coating preferably does not contain any additional dielectric layers. The geometric thickness of the upper anti-reflection layer is preferably 50 nm to 100 nm, particularly preferably 55 nm to 80 nm, in particular 60 nm to 70 nm. The geometric thickness of the lower anti-reflection layer is preferably 10 nm to 50 nm, particularly preferably 15 nm to 40 nm, in particular 20 nm to 35 nm. The geometric thickness of the adapter layer is preferably 5 nm to 30 nm, particularly preferably 8 nm to 12 nm.

[0045] In another embodiment of the present invention, a first lower dielectric layer (anti-reflection layer), a second lower dielectric layer (adaptive layer) and a third lower dielectric layer (refractive index increasing layer) are arranged below the conductive layer. Similarly, a first upper dielectric layer (anti-reflection layer), a second upper dielectric layer (adaptive layer) and a third upper dielectric layer (refractive index increasing layer) are arranged above the conductive layer. The refractive index of the anti-reflection layer, the adaptive layer and the refractive index increasing layer is at least 1.9. The refractive index increasing layer has a higher refractive index than the anti-reflection layer, preferably at least 2.1. The anti-reflection layer is preferably formed based on silicon nitride, the adaptive layer is based on zinc oxide, and the refractive index increasing layer is based on silicon-metal-mixed nitride, such as silicon-zirconium-mixed nitride or silicon-hafnium-mixed nitride. The adaptive layer preferably has a minimum distance from the silver layer, and the refractive index increasing layer is arranged between the adaptive layer and the anti-reflection layer. The following layer sequence, starting from the substrate, is produced: lower antireflection layer - lower refractive index-increasing layer - lower adaptation layer - silver layer - upper adaptation layer - upper refractive index-increasing layer - upper antireflection layer. The reflective coating preferably does not contain any additional dielectric layers. The geometric thickness of the upper antireflection layer is preferably 50 nm to 100 nm, particularly preferably 55 nm to 80 nm, in particular 60 nm to 70 nm. The geometric thickness of the lower antireflection layer is preferably 10 nm to 50 nm, particularly preferably 15 nm to 40 nm, in particular 20 nm to 35 nm. The geometric thickness of the adaptation layer is preferably 5 nm to 30 nm, particularly preferably 8 nm to 12 nm. The geometric thickness of the refractive index-increasing layer is preferably 5 nm to 30 nm, particularly preferably 5 nm to 15 nm.

[0046] Since the upper and lower dielectric layer sequences can be formed independently of one another, combinations of the above-described embodiments are also possible, wherein the upper dielectric layer / layer sequence is formed according to one embodiment and the lower dielectric layer / layer sequence is formed according to another embodiment. The following preferred layer sequence results (in each case starting from the substrate, i.e., from the surface on which the reflective coating is deposited):

[0047] - Lower anti-reflection layer – Silver layer – Upper anti-reflection layer

[0048] -Lower anti-reflection layer – silver layer – upper adaptation layer – upper anti-reflection layer

[0049] -Lower anti-reflection layer – silver layer – upper adaptation layer – upper refractive index increasing layer – upper anti-reflection layer -Lower anti-reflection layer – lower adaptation layer – silver layer – upper anti-reflection layer

[0050] -Lower anti-reflection layer – lower adaptive layer – silver layer – upper adaptive layer – upper anti-reflection layer -Lower anti-reflection layer – lower adaptive layer – silver layer – upper adaptive layer – upper refractive index increasing layer – upper anti-reflection layer

[0051] -Lower anti-reflection layer – lower refractive index increasing layer – lower adaptive layer – silver layer – upper anti-reflection layer -Lower anti-reflection layer – lower refractive index increasing layer – lower adaptive layer – silver layer – upper adaptive layer – upper anti-reflection layer

[0052] - Lower antireflection layer - Lower refractive index-increasing layer - Lower adaptation layer - Silver layer - Upper adaptation layer - Upper refractive index-increasing layer - Upper antireflection layer In one advantageous embodiment, the reflective coating includes at least one metallic barrier layer. This barrier layer can be arranged below and / or above the silver layer and is preferably in direct contact with the silver layer. The barrier layer is then located between the silver layer and the dielectric layer / layer sequence. The barrier layer serves to protect the silver layer from oxidation, particularly when the coated glass pane is subjected to temperature treatments, such as those typically encountered during bending processes. The geometric thickness of the barrier layer is preferably less than 1 nm, for example 0.1 nm to 0.5 nm. The barrier layer is preferably based on titanium or a nickel-chromium alloy.

[0053] The barrier layer only negligibly alters the optical properties of the reflective coating and is preferably present in all of the above-described embodiments. Particularly preferably, the barrier layer is arranged directly above the silver layer, i.e., between the silver layer and the upper dielectric layer(s), where it is particularly effective. The following preferred layer sequence results:

[0054] -Lower anti-reflection layer – silver layer – barrier layer – upper anti-reflection layer

[0055] -Lower anti-reflection layer – silver layer – barrier layer – upper adaptive layer – upper anti-reflection layer -Lower anti-reflection layer – silver layer – barrier layer – upper adaptive layer – upper refractive index increasing layer – upper anti-reflection layer

[0056] -Lower anti-reflection layer – lower adaptive layer – silver layer – barrier layer – upper anti-reflection layer -Lower anti-reflection layer – lower adaptive layer – silver layer – barrier layer – upper adaptive layer – upper anti-reflection layer -Lower anti-reflection layer – lower adaptive layer – silver layer – barrier layer – upper adaptive layer – upper refractive index increasing layer – upper anti-reflection layer

[0057] -Lower anti-reflection layer – Lower refractive index increasing layer – Lower adapting layer – Silver layer – Barrier layer – Upper anti-reflection layer

[0058] -Lower anti-reflection layer – lower refractive index increasing layer – lower adaptation layer – silver layer – barrier layer – upper adaptation layer – upper anti-reflection layer

[0059] -Lower anti-reflection layer – lower refractive index increasing layer – lower adaptive layer – silver layer – barrier layer – upper adaptive layer – upper refractive index increasing layer – upper anti-reflection layer

[0060] In each case, an additional barrier layer can optionally be arranged directly beneath the silver layer, ie between the silver layer and the lower dielectric layer(s).

[0061] The projector is arranged on the interior side of the windshield and illuminates the windshield above the interior-side surface of the inner glass pane. It is aligned with the HUD area and illuminates it to produce the HUD projection. According to the present invention, the radiation from the projector is predominantly p-polarized, i.e., it has a p-polarized radiation component greater than 50%. The higher the proportion of p-polarized radiation in the total radiation from the projector, the greater the intensity of the desired projected image and the less intense the unwanted reflections on the windshield surface. The p-polarized radiation component of the projector is preferably at least 70%, particularly preferably at least 80%, and especially at least 90%. In a particularly advantageous embodiment, the radiation from the projector is essentially purely p-polarized—i.e., the p-polarized radiation component is 100% or has only slight deviations. The polarization direction is specified herein with respect to the radiation incidence plane on the windshield. P-polarized radiation is radiation whose electric field oscillates in the incidence plane. S-polarized radiation is radiation whose electric field oscillates perpendicular to the incidence plane. The incidence plane is defined as a vector space spanned by the incidence vector and the surface normal of the windshield at the geometric center of the illumination area.

[0062] The radiation from the projector preferably strikes the windshield at an angle of incidence of 45° to 70°, in particular 55° to 70°. In one advantageous embodiment, the angle of incidence deviates from the Brewster angle by a maximum of 10°. The p-polarized radiation is then only negligibly reflected on the surface of the windshield, so that no ghost images are produced. The angle of incidence is the angle between the incident vector of the projector radiation and the interior-side surface normal in the geometric center of the HUD area (i.e., the surface normal on the exterior surface of the interior side of the windshield). In the case of soda-lime glass, the Brewster angle of the air-to-glass transition is 56.5°, which is typical for window panes. Ideally, the angle of incidence should be as close to this Brewster angle as possible. However, for example, an angle of incidence of 65°, which is typical for HUD projection devices, can also be used. This angle of incidence is easily achievable in vehicles and deviates only slightly from the Brewster angle, so that the reflection of the p-polarized radiation is only negligibly increased.

[0063] Since the reflection of the projector radiation occurs primarily at the reflective coating rather than at the outer glass pane surfaces, it is not necessary to arrange the outer glass pane surfaces at an angle to each other to avoid ghost images. Therefore, the outer surfaces of the windshield are preferably arranged essentially parallel to each other. For this purpose, the thermoplastic interlayer is preferably not wedge-shaped, but rather has a substantially constant thickness, particularly in the vertical direction between the upper and lower edges of the windshield, as is the case with the inner and outer glass panes. In contrast, a wedge-shaped interlayer has a variable, particularly increasing, thickness in the vertical direction between the upper and lower edges of the windshield. The interlayer is typically formed from at least one thermoplastic film. Since standard films are significantly more cost-effective than wedge films, the windshield is therefore more economical to manufacture.

[0064] The outer and inner panes are preferably made of glass, in particular soda-lime glass, as is common for window panes. However, in principle, the panes can also be made of other glass types (e.g., borosilicate glass, quartz glass, aluminosilicate glass) or transparent plastics (e.g., polymethyl methacrylate or polycarbonate). The thickness of the outer and inner panes can vary widely. Glass panes with a thickness of 0.8 mm to 5 mm, preferably 1.4 mm to 2.5 mm, are preferably used, for example, those with a standard thickness of 1.6 mm or 2.1 mm.

[0065] The outer pane, inner pane, and thermoplastic interlayer can be transparent and colorless, but can also be tinted or colored. In a preferred embodiment, the total transmittance through the windshield (including the reflective coating) is greater than 70%. The term total transmittance refers to the test method for light transmittance of motor vehicle glazing as specified in ECE-R 43, Annex 3, §9.1. The outer pane and inner pane can be independently unstressed, partially prestressed, or prestressed. If at least one of the panes is to be prestressed, this can be thermal or chemical.

[0066] In one advantageous embodiment, the outer pane is tinted or colored. This reduces the reflectivity of the windshield's exterior, making the appearance of the pane more pleasing to outside observers. However, to ensure the specified 70% light transmittance (total transmittance) of the windshield, the light transmittance of the outer pane should preferably be at least 80%, particularly preferably at least 85%. The light transmittance describes the proportion of radiation transmitted at an angle of incidence of 0° within the visible spectral range of 380 nm to 780 nm. The light transmittance can be determined using commercially available measuring instruments, such as spectrometers from Perkin Elmer, using methods known to those skilled in the art. The inner pane and the interlayer are preferably transparent, i.e., not tinted or colored. For example, green or blue tinted glass can be used as the outer pane.

[0067] The windshield is preferably curved in one or more directions in space, as is common for automotive glazing, with typical radii of curvature being from about 10 cm to about 40 m. However, the windshield can also be flat, for example, if it is intended as glazing for buses, trains or tractors.

[0068] The thermoplastic interlayer comprises at least one thermoplastic polymer, preferably ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), or polyurethane (PU), or mixtures, copolymers, or derivatives thereof, with PVB being particularly preferred. The interlayer is typically formed from a thermoplastic film. The thickness of the interlayer is preferably 0.2 mm to 2 mm, particularly preferably 0.3 mm to 1 mm.

[0069] The windshield can be produced by methods known per se. The outer and inner glass panes are laminated to one another via an interlayer, for example, by means of an autoclave method, a vacuum bag method, a vacuum ring method, a calendaring method, a vacuum laminator, or a combination thereof. The outer and inner glass panes are typically joined under the action of heat, vacuum, and / or pressure.

[0070] The reflective coating is preferably applied to the surface of the glass pane by physical vapor deposition (PVD), particularly preferably by cathode sputtering ("sputtering"), very particularly preferably by magnetic field-assisted cathode sputtering ("magnetron sputtering"). The coating is preferably applied before lamination. Instead of applying the reflective coating to the surface of the glass pane, it can, in principle, also be provided on a carrier film arranged in the interlayer.

[0071] If the windshield is to be curved, the outer and inner glass panes are preferably subjected to a bending process before lamination and preferably after the coating process. Preferably, the outer and inner glass panes are bent together (i.e., simultaneously and using the same tool) because this allows the shapes of the glass panes to be optimally matched to one another for subsequent lamination. Typical temperatures for the glass bending process are, for example, 500°C to 700°C. This temperature treatment also increases transparency and reduces the sheet resistance of the reflective coating.

[0072] The present invention also includes the use of a windshield formed according to the invention as a projection surface for a projection device for a head-up display, wherein the projector is directed onto the HUD area and its radiation is predominantly p-polarized. The above-described preferred embodiments apply accordingly to this use.

[0073] The present invention further includes the use of the projection device according to the invention as a head-up display (HUD) in a motor vehicle, in particular a passenger car or truck. Particularly preferably, the projection device is used as a head-up display (HUD) in combination with a sensor, in particular a camera, wherein the reflective coating is located in the sensor's beam path. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The present invention will be explained in more detail below with reference to the accompanying drawings and examples. The drawings are schematic and not to scale. The drawings do not limit the present invention in any way.

[0076] in:

[0077] Figure 1 shows a plan view of a projection device according to the invention as a flat display with a HUD area and a sensor area,

[0078] Figure 2 Shown along the section line AA' through Figure 1 The cross section of the projection device,

[0079] Figure 3 Shown along Figure 1 The section line AA' passes through a cross section of a composite glass pane according to another embodiment of a projection device according to the present invention,

[0080] Figure 4 shows a cross section through an embodiment of the reflective coating according to the invention on the inner glass pane,

[0081] Figure 5 The reflection spectra of the composite glass panes according to Example 3 and Comparative Examples 4 and 9 for p-polarized radiation are shown. DETAILED DESCRIPTION

[0082] Figure 1 and 2 A projection device according to the present invention for HUD is shown, wherein Figure 1 The plan view is shown in Figure 2 The figure shows the Figure 1 The projection device comprises a windshield 10, particularly a windshield of a passenger vehicle. It also includes a projector 4, which is directed at an area of ​​the composite glass pane 10. In this area, often referred to as the HUD area B, the projector 4 generates an image that, when the viewer's 5 eye is within the so-called eye-movement range E, is perceived by the viewer 5 (the vehicle driver) as a virtual image on the side of the composite glass pane 10 facing away from him. The windshield 10 is constructed from an outer glass pane 1 and an inner glass pane 2, which are connected by a thermoplastic interlayer 3. Its lower edge U faces downward toward the passenger vehicle's engine, while its upper edge O faces upward toward the vehicle roof. In the installed position, the outer glass pane 1 faces the exterior, while the inner glass pane 2 faces the vehicle interior. A reflective coating 20 is disposed between the inner sides of the outer glass pane 1 and the inner glass pane 2. It can be arranged on the inner side of the outer pane 1 or on the inner side of the inner pane 2 or integrated into the thermoplastic intermediate layer 3 .

[0083] Figure 3 One embodiment of a windshield 10 formed according to the present invention is shown. The portion of the projection device extending beyond the windshield 10 corresponds to Figure 1 and Figure 2 And in Figure 3 (not shown in the figure). The outer glass pane 1 has an outer surface I facing the outside environment in the installed position (also referred to as the outer side of the outer glass pane) and an interior-side surface II facing the interior space in the installed position (also referred to as the inner side of the outer glass pane). Similarly, the inner glass pane 2 has an outer surface III facing the outside environment in the installed position (also referred to as the inner side of the inner glass pane) and an interior-side surface IV facing the interior space in the installed position (also referred to as the outer side of the inner glass pane). The outer glass pane 1 and the inner glass pane 2 are composed, for example, of soda-lime glass. The thickness of the outer glass pane 1 is, for example, 2.1 mm, and the thickness of the inner glass pane 2 is, for example, 1.6 mm or 2.1 mm. The intermediate layer 3 is formed, for example, of a PVB film and has a thickness of 0.76 mm. This PVB film has a substantially constant thickness, except for any surface roughness common in the art—it is not formed as a so-called wedge film.

[0084] The outer side surface III of the inner pane 2 (outside of the inner pane) has a reflective coating 20 according to the invention, which is provided as a reflective surface for projector radiation (and possibly additionally as an IR-reflective coating).

[0085] According to the present invention, the radiation from projector 4 is p-polarized, in particular, substantially pure p-polarized. Since projector 4 illuminates windshield 10 at an angle of incidence close to the Brewster angle of approximately 65°, the projector radiation is only negligibly reflected from outer surfaces I, IV of composite glass pane 10. In contrast, reflective coating 20 according to the present invention is optimized for reflecting p-polarized radiation. It serves as a reflective surface for the radiation from projector 4 and is used to produce the HUD projection.

[0086] Figure 4 The layer sequence of one embodiment of a reflective coating 20 according to the present invention is shown. The reflective coating 20 is a stack of thin layers. The reflective coating 20 comprises a silver-based conductive layer 21. A metallic barrier layer 24 is arranged directly above the conductive layer 21. Above the conductive layer 21, an upper dielectric layer sequence is arranged, which consists, from bottom to top, of an upper adapting layer 23b, an upper refractive index-increasing layer 23c, and an upper antireflection layer 23a. Below the conductive layer 21, a lower dielectric layer sequence is arranged, which consists, from top to bottom, of a lower adapting layer 22b, a lower refractive index-increasing layer 22c, and a lower antireflection layer 22a.

[0087] The layer structure shown is provided only as an example. Therefore, the dielectric layer sequence can also include more or fewer layers, as long as at least one dielectric layer is present above and below the conductive layer 21. The dielectric layer sequence also does not have to be symmetrical. Exemplary materials and layer thicknesses can be found in the examples below. The dielectric and silver layers shown were deposited by magnetron sputtering.

[0088] Tables 1a and 1b show the layer sequence of a windshield 10 having a reflective coating 20 on the outer side III of the inner pane 2 according to inventive examples 1 to 8, as well as the materials and geometric layer thicknesses of the individual layers. The dielectric layers can be doped independently of one another, for example with boron or aluminum.

[0089] Table 1a

[0090]

[0091] Table 1b

[0092]

[0093] For comparison, comparative examples 1 to 8, which do not conform to the features according to the invention, were investigated. Their layer sequences are shown in Tables 2a and 2b.

[0094] Table 2a

[0095]

[0096] Table 2b

[0097]

[0098] The difference between the examples and the comparative examples lies primarily in the ratio of the optical thickness of the upper dielectric layer sequence to the optical thickness of the lower dielectric layer sequence. The optical thickness is each obtained as the product of the geometric thickness shown in Tables 1a, 1b and 2a, 2b and the refractive index, with a value of 2.0 being used for SiN, a value of 2.2 being used for SiZrN, and a value of 2.0 being used for ZnO. The optical thicknesses and their ratios are summarized in Tables 3a, 3b, and 3c. The ratio φ describes the ratio of the optical thickness of the upper dielectric layer 23a or layer sequence 23a, 23b, and optionally 23c to the optical thickness of the lower dielectric layer 22a or layer sequence 22a, 22b, and optionally 22c. In addition to the optical thickness and the optical thickness ratio, Tables 3a, 3b, and 3c also show the polarization ratio of p-polarized radiation to s-polarized radiation when transmitted at different transmission angles and the total transmittance T in the visible range of the spectrum. L According to Table 3a, the transmission angle used in the investigation of the polarization ratios was 61°, while Table 3b shows the polarization ratios of the layer stacks at 67° and in Table 3c at 55°.

[0099] Table 3a

[0100]

[0101] Table 3b

[0102]

[0103] Table 3c

[0104]

[0105] In order for a windscreen according to the invention to be legally permitted as a windscreen, the total transmittance T through the windscreen (including the reflective coating) must be 100% in accordance with ECE-R43, Annex 3, §9.1. L It must be at least 70%. At the same time, in order for the HUD projection device to be compatible with camera systems, the polarization ratio of p-polarized radiation to s-polarized radiation in transmission must be as high as possible. In particular, a polarization ratio of at least 1.41 should be achieved at a transmission angle of 61°, at least 1.59 at a transmission angle of 67°, and at least 1.28 at a transmission angle of 55°. This facilitates meeting the technical specifications required in common camera systems. In Examples 1 to 8, where the ratio φ falls within the scope of the present invention, a good polarization ratio is achieved at a total transmittance of at least 70%. Therefore, the HUD projection device according to the present invention is particularly suitable for use with camera systems.

[0106] Figure 5 Shown with Figure 3 Reflection spectra of a composite glass pane 10 with a basic structure are shown, with Example 3 according to the invention according to Table 1a and Comparative Example 4 not according to the invention according to Table 2a showing the layer structures according to the invention and not according to the invention, respectively. To better illustrate the spectra of Example 3 and Comparative Example 4, the reflection spectrum of a composite glass pane with a layer structure not according to the invention according to Comparative Example 9, according to Tables 4a and 4b, is also shown. The reflection spectra were recorded using a light source emitting p-polarized radiation with uniform intensity within the observed spectral range, with illumination from above the inner pane 2 (so-called interior-side reflection) at an angle of incidence of 65° relative to the surface normal on the interior side. This reflection measurement thus resembles the conditions in a projection setup.

[0107] Table 4a

[0108]

[0109] Table 4b

[0110] Optical thickness of the upper dielectric layer sequence Optical thickness of the lower dielectric layer sequence Ratio φ Comparative Example 9 102 142 0.72 .

[0111] As can be seen from the graphical display of the spectra, Example 3 according to the invention, which has an inventive ratio of optical thicknesses of the upper and lower dielectric layers or layer sequences, exhibits a similar curve to Comparative Example 4, not according to the invention. In both cases, relatively smooth spectra are achieved in the interesting spectral range of 400 nm to 680 nm. To better categorize them, the spectrum of a composite glass pane according to Comparative Example 9, not according to the invention, is shown. Although Comparative Example 9 also achieves relatively high average reflectance values, the spectrum fluctuates significantly within the relevant spectral range of 400 nm to 680 nm, which can lead to undesirable color shifts in the HUD image and a poorer color impression of the glass pane for the viewer. In contrast, the smoother spectra of Example 3 and Comparative Example 4 produce a more color-neutral HUD projection. Furthermore, the overall color impression of the glass pane is improved. A comparison of Example 3 according to the invention and Comparative Example 4 shows that the favorable HUD properties of the composite glass pane are retained even after the layer structure according to the invention has been optimized for camera compatibility. Therefore, the HUD projection device according to the invention is particularly suitable for use with camera systems.

[0112] All glass panels have a light transmittance greater than 70%, so they can be used as windshields.

[0113] List of reference numerals:

[0114] (10) Windshield

[0115] (1) Outer glass panel

[0116] (2) Inner glass panel

[0117] (3) Thermoplastic intermediate layer

[0118] (4) Projector

[0119] (5) Viewers / vehicle drivers

[0120] (6) Sensor

[0121] (20)Reflective coating

[0122] (21) Conductive layer

[0123] (22a) First lower dielectric layer / anti-reflection layer

[0124] (22b) Second lower dielectric layer / adaptive layer

[0125] (22c) Third lower dielectric layer / refractive index increasing layer

[0126] (23a) First upper dielectric layer / anti-reflection layer

[0127] (23b) Second upper dielectric layer / adaptive layer

[0128] (23c) Third upper dielectric layer / refractive index increasing layer

[0129] (24) Metal barrier layer

[0130] (O) Upper edge of the windshield 10

[0131] (U) Lower edge of windshield 10

[0132] (B) HUD area of ​​the windshield 10

[0133] (E) Eye movement range

[0134] (S) Sensor area of ​​windshield 10

[0135] (I) The outer surface of the outer glass sheet 1 away from the intermediate layer 3

[0136] (II) The inner space side surface of the outer glass plate 1 facing the intermediate layer 3

[0137] (III) The outer surface of the inner glass sheet 2 facing the intermediate layer 3

[0138] (IV) The interior space side surface of the inner glass sheet 2 that is remote from the intermediate layer 3 .

Claims

1. A projection device for a head-up display (HUD), comprising at least - a windshield (10) with a HUD region (B), comprising an outer glass pane (1) with an outer side (I) and an inner side (II) and an inner glass pane (2) with an inner side (III) and an outer side (IV), wherein the inner side (II) of the outer glass pane (1) and the inner side (III) of the inner glass pane (2) are connected to each other via a thermoplastic intermediate layer (3); and - a projector (4) directed towards the HUD area (B); in - the radiation of the projector (4) is predominantly p-polarized, and - the windshield (10) has a reflective coating (20) suitable for reflecting p-polarized radiation; And among them the reflective coating (20) has exactly one conductive layer (21) based on silver, - a lower dielectric layer (22a) or layer sequence (22a, 22b, 22c) is arranged below the electrically conductive layer (21) and has a refractive index of at least 1.9, - an upper dielectric layer (23a) or layer sequence (23a, 23b, 23c) is arranged above the electrically conductive layer (21) and has a refractive index of at least 1.9, - the ratio of the optical thickness of the upper dielectric layer (23a) or layer sequence (23a, 23b, 23c) to the optical thickness of the lower dielectric layer (22a) or layer sequence (22a, 22b, 22c) is from 2.10 to 3.20, and - the reflective coating (20) does not include a dielectric layer whose refractive index is less than 1.9, The windshield (10) comprises a sensor region (S) in which radiation passes through the reflective coating (20) and can be detected by a sensor (6) provided in the sensor region (S).

2. A projection device according to claim 1, wherein the ratio of the optical thickness of the upper dielectric layer (23a) or layer sequence (23a, 23b, 23c) to the optical thickness of the lower dielectric layer (22a) or layer sequence (22a, 22b, 22c) is 2.14 to 3.

10.

3. A projection device according to claim 2, wherein the ratio of the optical thickness of the upper dielectric layer (23a) or layer sequence (23a, 23b, 23c) to the optical thickness of the lower dielectric layer (22a) or layer sequence (22a, 22b, 22c) is 2.50 to 2.

97.

4. The projection device as claimed in claim 1, wherein the sensor (6) is arranged in the sensor region (S) on the outer side (IV) of the inner glass pane (2). 5 . The projection device according to claim 4 , wherein the sensor ( 6 ) is based on ultrasound, radar, lidar and / or camera technology.

6. The projection device according to any one of claims 1 to 2, wherein: - Arrangement below the conductive layer (21) of exactly one lower dielectric layer (22a) having a refractive index of at least 1.9, and / or - Arranged above the conductive layer (21) is exactly one upper dielectric layer having a refractive index of at least 1.

9.

7. The projection device according to any one of claims 1 to 2, wherein - arranging a first lower dielectric layer (22a) and a second lower dielectric layer (22b) having a refractive index of at least 1.9 below the conductive layer (21), and / or - a first upper dielectric layer (23a) and a second upper dielectric layer (23b) having a refractive index of at least 1.9 are arranged above the conductive layer (21).

8. The projection device according to any one of claims 1 to 2, wherein - arranging a first lower dielectric layer (22a), a second lower dielectric layer (22b) and a third lower dielectric layer (22c) having a refractive index of at least 1.9 below the conductive layer (21), and / or - a first upper dielectric layer (23a), a second upper dielectric layer (23b) and a third upper dielectric layer (23c) having a refractive index of at least 1.9 are arranged above the conductive layer (21).

9. The projection device according to claim 1 , wherein the reflective coating ( 20 ) comprises at least one metal barrier layer ( 24 ), which is arranged above and / or below the conductive layer ( 21 ) and has a geometric thickness of less than 1 nm.

10. The projection device according to claim 1, wherein the outer glass pane (1) is tinted or colored and has a light transmission of at least 80%.

11. The projection device as claimed in claim 1, wherein the radiation of the projector (4) is substantially purely p-polarized.

12. The projection device according to claim 1, wherein the radiation of the projector (4) impinges on the windshield (10) at an angle of incidence of 55° to 70°.

13. The projection device according to any one of claims 1 to 2, wherein the conductive layer (21) has a geometric thickness of 10 nm to 14 nm.

14. The projection device according to claim 1, wherein the outer surfaces (I, IV) of the windshield (10) are arranged substantially parallel to one another.

15. The projection device according to claim 1, wherein the reflective coating (20) is arranged on the surface (II, III) of the outer glass pane (1) or the inner glass pane (2) facing the intermediate layer (3) or in the intermediate layer (3).

Images